High pressure and other characteristics into a material trends of metal bellows valve
- Jan 27, 2018 -

    Valve is suitable for the production of corrugated pipe, and material must have good plasticity, high elastic limit, tensile strength and fatigue strength, good welding performance, stable elastic properties. Austenitic stainless steel is widely used to make bellows because of these performance characteristics.


    In metal bellows valves, a metal bellows assembly provides an axially movable metal housing between the valve stem and the process fluid in the valve body to form a dynamic seal. Bellows withstands compression and extension of the valve stem while under pressure, temperature and corrosion of the medium, ensuring zero leakage over the life of the valve. With the widespread application of bellows in the valve industry, the technical requirements for bellows are also continuously increasing. Valve with metal bellows continue to high pressure, high temperature, corrosion-resistant and long-life direction.


    Valve with corrugated pipe material requirements

    Suitable for the production of corrugated pipe materials must have good plasticity, high elastic limit, tensile strength and fatigue strength, good weldability, stable elastic properties. Austenitic stainless steel is widely used to make bellows because of these performance characteristics.


    High pressure

    Pressure is the basic requirements of the valve and bellows, but with the valve pressure level increases, the bellows wall thickness increases and increased stiffness to the valve opening and bellows have increased the difficulty of manufacturing. Bellows manufacturers generally do not simply increase the wall thickness, but by increasing the number of layers to improve product pressure resistance, while reducing the axial stiffness of the bellows and reduce the valve opening force. Nominal pressure 15MPa (900lb) below austenitic stainless steel bellows wall thickness is generally 0.1 ~ 0.3mm, the number of layers 1-6. The pressure level of corrugated pipe has a certain versatility, has formed a series of products. When the pressure reaches 25MPa (1500lb) above, according to the valve diameter and temperature to choose the right material, by the bellows professional manufacturer design and production.


    Preservative

    Corrosion resistance of non-metallic materials, excellent performance, fluorine plastic anti-corrosion valve widely used, PTFE bellows valve also has some applications. However, due to non-metallic materials, low strength and heat resistance, the general use temperature does not exceed 150 ℃, the scope of application is limited. Austenitic stainless steels represented by 304 and 316L can handle corrosive corrosive conditions. However, when dealing with wet chlorine corrosion in chlor-alkali industries and other harsh corrosive conditions, corrosion-resistant alloys with excellent corrosion resistance must be used material. Corrosion resistance of the corrosion resistance of the alloy and the crevice corrosion resistance commonly used resistance to corrosion equivalent (PRE) value characterization, PRE value calculated according to equation (1).


    PRE =% Cr + 3.3 ×% Mo + 16 ×% N (1)


    The higher the PRE value, the higher the critical crevice corrosion temperature (CCT) and the critical pitting temperature (CPT) of the alloy. It can be seen from Table 1 that the PRE values of several corrosion-resistant alloys are much higher than the PRE values of 304 and 316L.


    High temperature

    The valve temperature above 450 ℃ is called high temperature valve. Austenitic stainless steel recommended working temperature up to 400 ℃, so the high temperature valve must use high temperature alloy materials.